‘(Meth)acrylic acid’ is the collective term including ‘methacrylic acid’ and ‘acrylic acid’. In the present invention, the term ‘(meth)acrylic acid’ is used with the above meaning.
Generally, (meth)acrylic acid esters are prepared by esterification of alkanols and (meth)acrylic acid in the presence of strong acids.
In general, synthesis of (meth)acrylic acid is performed in facilities comprising distillation columns, extractors, and mixers. In the process, heat exchange is primarily carried out with a plate type or tube-bundle type of spiral heat exchanger, or a rotary evaporator.
The problem of preparing (meth)acrylic acid and (meth)acrylic acid esters by the conventional method is that unwanted radical polymerization is caused by light or heat. In particular, in esterification, control of temperature for avoiding the unwanted radical polymerization and obtaining desired esterification rate is complicated. Because this problem also occurs in purification of (meth)acrylic acid or (meth)acrylic acid esters, a high-temperature boiler involved in the process should be separated from a low-temperature boiler and separation of esters should be done within an appropriate temperature range.
If not, it is highly plausible that unwanted polymerization of (meth)acrylic acid and (meth)acrylic acid esters takes place. Indeed, resultant polymers are deposited and cause contamination in facility parts including pipes, pumps, evaporators, distillation columns, heat exchangers, and condensers.
Polymerization inhibitors may be added when mixing reactants in order to prevent such unwanted polymerizations, but empirically and theoretically, it is impossible to prevent all polymerization from occurring inside the reactor. Thus, most manufacturing processes of (meth)acrylic acid or (meth)acrylic acid esters thus far have operated the reaction apparatus for weeks or tens of weeks, and the operation has then been stopped to clean off unwanted polymers and then re-operate the apparatus.
Also, highly viscous and high molecular weight polymer compounds resulting from the Michael reaction of (meth)acrylic acid and (meth)acrylate, which deposit at processing apparatuses, pose another problem. These polymer compounds have previously been removed manually or by using adequate solvents, which is not only ineffective and costly but also causes environmental pollution.
Generally, organic solvents such as dimethylformamide, dibutylformamide, dimethylacetamide, sulfolane, N-methylpyrrolidone, etc., have been used to clean processing apparatuses. However, as with manual cleaning, the polymers are not completely removed by this method, thereby reducing productivity and causing production efficiency losses.
In circulation cleaning using the conventional cleaning solutions, incomplete cleaning of polymer compounds may result in frequent side reactions during re-operation and their shortened occurring periods, in spite of using alkali metal hydroxide solutions and drying processes.
Accordingly, an improved cleaning solution for facility parts and a cleaning method capable of overcoming the problems of the conventional cleaning materials, methods, and procedures with regard to preparation of (meth)acrylic acid and/or (meth)acrylic esters are urgently needed.